In recent years, computers have become more infected with viruses that invade a computer and cause some damage. This is because a widely popularized communications network serves as an infection route of viruses. Therefore, antivirus measure is essential especially to computers that can transmit/receive data via a communications network.
The basic antivirus measure is to install antivirus software, which is software for removing viruses, in a computer. However, since it is difficult to take measures against new types of viruses, the infection of viruses cannot be completely prevented even if antivirus software is used. Virtual machines (VMs) are also used as another antivirus measure.
Virtual machines are one of virtualization techniques of computers. In virtual machines, different programs can be operated on virtualized hardware (resources). By using the virtual machines, a plurality of operating systems (OSes) can be operated on one computer. The programs on each virtual machine operate in independent address spaces, and do not directly interfere with one another. Accordingly, even if one virtual machine is infected with a virus, the other virtual machines are not infected with this virus. The virtual machines that are not infected with the virus can continue to operate. As a result, influences exerted by the infection of the virus can be more reduced by using the virtual machines.
Each virtual machine completely independently operates under a one-program execution environment. Therefore, antivirus software is conventionally prepared for each virtual machine when it is used.
Antivirus software generally detects viruses by referencing a definition file. The definition file stores pattern data of each virus. Accordingly, the definition file is also called a pattern file. Since a lot of viruses have been already found, the definition file has an enormous amount of data at present. This also leads to a significant increase in resources consumed by antivirus software, and a heavier load imposed on virtualized hardware, if the antivirus software is introduced into each virtual machine.
Both the increase in consumed resources and the heavier load imposed on hardware require higher specifications for the responsive operations of a computer. If a service is provided by the computer, the required higher specifications degrade the quality of the provided service.
Additionally, when the antivirus software is executed, the operations of the system sometimes become unstable. The definition file must be frequently updated to take measures against new types of viruses that appear one after another. Therefore, updating the definition file imposes a load on hardware, and a transmission/reception of data for an update via a communications network increases the amount of traffic. Also for these reasons, the responsive operations of the computer are hindered.
As a result, the viewpoint of causing a computer to operate more responsively is important as antivirus measures.
As referential technical documents, Japanese National Publication of International Patent Application No. 2008-500653, Japanese Laid-open Patent Publication No. 2004-361994, and Japanese Laid-open Patent Publication No. 2002-342106 can be cited.